1. Field of the Invention
The present invention relates to a particle monitoring system and method for a head disk assembly (HDA) to detect a head disk interface (HDI) event.
2. Description of the Prior Art and Related Information
A huge market exists for disk drives for mass-market host computer systems such as servers, desktop computers, and laptop computers, as well as small form factor (SFF) disk drives for use in mobile computing devices (e.g. personal digital assistants (PDAs), cell phones, etc.). To be competitive, a disk drive should be relatively inexpensive and provide substantial capacity, rapid access to data, and reliable performance.
Satisfying these competing constraints of low-cost, small size, high capacity and reliability requires innovation in each of a drive's numerous components and in the methods of assembling and testing disk drives. Typically, the main assemblies of a disk drive are a head disk assembly (HDA) and a printed circuit board assembly (PCBA).
FIG. 1 shows the principal components of an example of a disk drive 100. With reference to FIG. 1, the disk drive 100 comprises a head disk assembly (HDA) 144 and a printed circuit board assembly (PCBA) 114. The HDA 144 includes a disk drive enclosure comprising a base 116 and a cover 117 attached to the base 116 that collectively house a disk stack 123 that includes one or a plurality of magnetic disks (of which only a first disk 111 and a second disk 112 are shown), a spindle motor 113 attached to the base 116 for rotating the disk stack 123, an HSA 120, and a pivot bearing cartridge 184 that rotatably supports the head stack assembly (HSA) 120 on the base 116. The spindle motor 113 rotates the disk stack 123 at a constant angular velocity.
The HSA 120 comprises a swing-type or rotary actuator assembly 130, at least one head gimbal assembly (HGA) 110, and a flex circuit cable assembly 180. The rotary actuator assembly 130 includes a body portion 140, at least one actuator arm 160 cantilevered from the body portion 140, and a coil portion 150 cantilevered from the body portion 140 in an opposite direction from the actuator arm 160. The actuator arm 160 supports the HGA 110 that, in turn, supports the slider(s). The flex cable assembly 180 may include a flex circuit cable and a flex clamp 159.
The HSA 120 is pivotally secured to the base 116 via the pivot-bearing cartridge 184 so that the slider at the distal end of the HGA 110 may be moved over the surfaces of the disks 111, 112. The pivot-bearing cartridge 184 enables the HSA 120 to pivot about a pivot axis, shown in FIG. 1 at reference numeral 182. The storage capacity of the HDA 144 may be increased by, for example, increasing the track density (the TPI) on the disks 111, 112 and/or by including additional disks in the disk stack 123 and by an HSA 120 having a vertical stack of HGAs 110 supported by multiple actuator arms 160.
The “rotary” or “swing-type” actuator assembly comprises body portion 140 that rotates on the pivot bearing 184 cartridge between limited positions, coil portion 150 that extends from one side of the body portion 140 to interact with one or more permanent magnets 192 mounted to back irons 170, 172 to form the voice coil motor (VCM), and the actuator arm 160 that supports the HGA 110. The VCM causes the HSA 120 to pivot about the actuator pivot axis 182 to cause the slider and the read write transducers thereof to sweep radially over the disk(s) 111, 112.
After the HDA 144 and the PCBA 114 are mated, the disk drive typically undergoes a variety of extensive tests and procedures to configure and validate the proper operation of the disk drive in a disk drive testing platform at a disk drive testing factory. This disk drive testing is a major expense in the cost of a disk drive.
A significant cost driver in disk drive testing is that there may be pre-existing media defects on one or more of the disks of a disk drive. These defects are typically not discovered until self-testing of the disk drive, which occurs as part of a configuration and validation process during the disk drive testing. During this testing, if a pre-existing media defect is discovered, this may result in a failure of the disk drive and consequently disk drive yield loss. Thus, the disk drive with the latent defect has utilized valuable disk drive testing time and space in the disk drive test platform. Even worse, the latent defect may not be discovered, and the disk drive may be shipped with the media defect only to be returned later by an unhappy customer.
These types of media defects typically occur due to a head disk interaction (HDI) in which the head contacts the disk. Further, when an HDI event occurs, particles, such as metal flakes, are created that can further damage the disk media as well as the read/write heads of the disk and other components of the disk drive.
HDI events may occur at a number of points in the disk drive assembly process prior to testing. For example, in the course of assembling the HDA, the head(s) are merged with the disk(s) during an operation known as a “head-disk merge operation.” Unfortunately, during the head-disk merge one or more heads may contact the disk media, creating a potential reliability or yield problem from resultant media defects or other particle related damage.
HDI events may also occur after the head-disk merge operation, but before disk drive testing, during servo-writing of the disk media. During internal servo-writing, a servo writer typically controls the HDA, such that the actuator arm of the HDA is rotated to position the head radially over the disk in order to write servo sectors onto the disk based upon an output clock that has been processed by timing circuitry. During servo-writing, servo information is written in a plurality of servo sectors that are angularly spaced from one another and that are interspersed between data sectors around each track of each disk. This special servo information may be utilized by the disk drive to determine the position of the head by a servo control system of the disk drive. However, during this internal HDA servo-writing process, previously-described HDI events may occur due to the head contacting the disk media.
HDI events may also occur during external servo-writing, in which the servo information is written to a disk utilizing an external servo writer before the disk is assembled into the disk drive.
Thus, there are many points during the assembly of a disk drive in which an HDI event may occur, causing media defects to one or more disks.